Study On Heat Storage And Heat Transfer Of Phase Change Thermal Storage Cement Based Materials And Phase Change Wall

With the increasing shortage of energy supply,reducing building energy consumption and promoting green buildings have attracted more and more attention.The use of traditional building insulation materials on the building envelope helps to improve the thermal insulation capacity of the envelope structure,but this method has a poor effect on the improvement of the heat storage capacity of the envelope structure.Compared with traditional building thermal insulation materials,phase change building materials that use form stable composite phase change materials as "thermal functional components" can participate in the storage and release of building thermal energy.It is of great significance to promote the phase change materials in buildings for saving building energy consumption and improving building thermal comfort.At present,although phase change building materials have shown good application prospects in the field of building energy conservation,the research on the preparation process,heat transfer characteristics and impact of phase change building materials on building energy consumption needs to be further improved.By combining numerical simulation and experiment,the modification process and thermal properties of inorganic mineral-based form stable composite phase change materials were studied and the combination of form stable composite phase change materials and cement mortar were optimized.The influence of form stable composite phase change materials on the heat transfer characteristics of phase change thermal storage mortar and phase change energy storage wall was also explored.In addition,the optimal layout and application area of phase change thermal storage mortar were analyzed.The main research contents and conclusions are shown as follows:(1)Silane modified attapulgite was used to adsorb paraffin to prepare a paraffin/modified attapulgite form stable composite phase change material.The melting temperature and solidification temperature of the composite phase change material are 25.7 °C and 23.3 °C,and the latent heat of melting and solidification are 83.4J/g and 79.7J/g,respectively.Compared with unmodified attapulgite,the latent heat of melting and solidification of the composite phase change material prepared by modified attapulgite increased by 42.8% and 43.3%,respectively.By studying the effect of paraffin/modified attapulgite form stable composite phase change material on the performance of cement mortar,it is found that the strength and thermal conductivity of the mortar decrease with the increase of the content of the composite phase change material.When the content of form stable composite phase change material is is 9% of the cement mass,the 28 d compressive strength and thermal conductivity of mortar decrease by47.4% and 37.5%,respectively.(2)Paraffin/modified attapulgite form stable composite phase change material is combined with mortar in the form of mineral admixture,which has a great influence on the strength of mortar.In order to optimize the combination mode of form stable composite phase change material and mortar,using acid-modified expanded vermiculite(a EV)as support material,diatomite(DI)as secondary coating material,a paraffin/a EV-DI form stable composite phase change material that can be used as fine aggregate was prepared.The melting temperature and solidification temperature of this composite phase change material are 26.2 °C and 24.3 °C,respectively,the latent heat of melting and solidification are 91.2J/g and 87.1J/g,and the thermal conductivity is 0.21W/m·K.Compared with unmodified paraffin/expanded vermiculite form stable composite phase change material,the latent heat of paraffin/a EV-DI form stable composite phase change material is increased by 23.9%,and the influence on mortar strength is weakened.In addition,adding paraffin/a EV-DI form stable composite phase change material to the mortar can also reduce the thermal conductivity and improve the thermal regulation ability.(3)The heat transfer model of phase change thermal storage mortar and phase change wall was established.The influence of the content and thermophysical parameters of paraffin/a EVDI form stable composite phase change material on the heat transfer process of phase change thermal storage mortar and phase change wall was calculated by FLUENT software.The research result shows that,the effective thermal conductivity of phase change thermal storage mortar decreases with increasing the content of form stable composite phase change material.Under the condition of a certain content,changing the particle size distribution of form stable composite phase change material has little effect on the thermal conductivity of mortar.In the transition season,when the phase change temperature of the form stable composite phase change material is close to the average indoor air temperature(25℃),the phase change wall has the best thermal adjustment ability;in summer,when the phase change temperature is close to the cooling temperature(26℃),the thermal insulation effect of phase change wall is the best;in winter,when the phase change temperature is close to the heating temperature(18℃),the phase change wall has the best insulation effect.Under the condition that the volume fraction of the form stable composite phase change material is 50%,when the latent heat of the form stable composite phase change material is more than 120J/g,the energy saving effect of the phase change wall is better in winter and summer.Increasing the thermal conductivity of form stable composite phase change material can improve the thermal regulation effect of phase change wall in transition season,but it will damage the thermal insulation effect of phase change wall in winter and summer.(4)By optimizing the mixing ratio of the thermal storage mortar,an expanded vermiculitebased phase change thermal storage mortar with high content of form stable composite phase change material and strength meeting the requirements of the building envelope structure was prepared.Subsequently,the self-made full scale testing room was used to comprehensively evaluate the temperature regulation and energy-saving effect of this mortar in the whole year.The results show that when the air conditioner is off,the expanded vermiculite based phase change thermal storage mortar has no thermal regulation ability in winter,and can reduce the temperature fluctuation of the testing room by up to 1.8 °C in summer and 3.6 °C in transition season.When the air conditioner is on,the expanded vermiculite based phase change thermal storage mortar can save the power consumption of the air conditioner in winter and summer,and the highest power saving rate is 11.1% in summer and 12.9% in winter.(5)By using Energy Plus software,the influence of the layout of expanded vermiculite based phase change thermal storage mortar on building energy consumption was studied and the applicability of this mortar in different climate areas was analyzed.The results show that,compared with the roof,the expanded vermiculite based phase change thermal storage mortar is more suitable to be arranged inside the exterior wall or the interior wall of the building;the best construction thickness of thermal storage mortar in building is 2cm-3cm,and the best application climate area is hot summer and cold winter area.